diff --git a/lib/tag_sanitizer.rb b/lib/tag_sanitizer.rb
new file mode 100644
index 000000000..f44b06adf
--- /dev/null
+++ b/lib/tag_sanitizer.rb
@@ -0,0 +1,17 @@
+class TagSanitizer
+
+  DISALLOWED_STRINGS = %w(? < > = /)
+
+  def sanitize_tag(tag)
+    tag = tag.dup
+    DISALLOWED_STRINGS.each do |s|
+      tag.gsub!(s, '')
+    end
+    tag
+  end
+
+  def sanitize_tag_list(tag_list)
+    tag_list.map { |tag| sanitize_tag(tag) }
+  end
+
+end
diff --git a/spec/lib/tag_sanitizer_spec.rb b/spec/lib/tag_sanitizer_spec.rb
new file mode 100644
index 000000000..e1fd6499b
--- /dev/null
+++ b/spec/lib/tag_sanitizer_spec.rb
@@ -0,0 +1,23 @@
+require 'rails_helper'
+
+describe TagSanitizer do
+
+  subject { described_class.new }
+
+  describe '#sanitize_tag' do
+    it 'allows regular text, even spaces' do
+      expect(subject.sanitize_tag('hello there')).to eq('hello there')
+    end
+
+    it 'filters out dangerous strings' do
+      expect(subject.sanitize_tag('user_id=1')).to eq('user_id1')
+    end
+  end
+
+  describe '#sanitize_tag_list' do
+    it 'returns a new tag list with sanitized tags' do
+      expect(subject.sanitize_tag_list(%w{x=1 y?z})).to eq(%w(x1 yz))
+    end
+  end
+
+end